Iodothyronine polymers

ABSTRACT

Iodothyronine polymers having a plurality of recurring units of formula I    &lt;IMAGE&gt;  I  in which A is iodo and B, C and D are independently H or iodo are described. Polymers in which A and C are iodo and B and D are independently H or iodo and in which substantially all of the recurring units are L-stereoisomers, have utility in treating thyroid hormone deficiencies.

This application is a continuation of application Ser. No. 07/854,671,filed 24 Jun. 1992, now abandoned, which is a continuation in part ofapplication Ser. No. 07/430,990, filed Nov. 3, 1989, now abandoned.

This invention relates to iodothyronine polymers which have utility inthe treatment of thyroid hormone deficiencies, to pharmaceuticalcompositions containing iodothyronine polymers and to the use ofiodothyronine polymers in the treatment of thyroid hormone deficiencies.The iodothyronine polymers of the present invention contain recurringunits linked by --NHCO-- bridging groups and are therefore polypeptides.

Thyroid hormone deficiencies are disease states in which insufficientthyroid hormone is released in the body causing a slowing down of allthe metabolic processes of the body and, in children, causing poormental and physical development. Dessicated thyroid glands obtained fromthe ox, sheep or pig have been used for many years to treat thyroidhormone deficiencies. However the actual thyroid hormone dose fromdessicated thyroid glands is difficult to regulate due to variations iniodine content between preparations. More recently syntheticlevothyroxine (LT₄) has been used to treat thyroid hormone deficiencies.

The present invention provides a substantially pure syntheticiodothyronine polymer having a plurality of recurring units, which maybe the same or different, of formula I ##STR2## in which A is iodo andB, C and D are independently H or iodo. In preferred iodothyroninepolymers substantially all of the recurring units of formula I are inthe same stereoisomeric form. In particularly preferred iodothyroninepolymers substantially all of the recurring units of formula I areL-stereoisomers. In preferred iodothyronine polymers A and C are iodoand B and D are independently H or iodo. In particularly preferrediodothyronine polymers A and C are iodo and at least one of B and D isiodo. The average number of the recurring units may vary from about 5 toabout 400, preferably from about 10 to about 400, more preferably fromabout 20 to about 200, or from about 30 to about 150 or from about 80 toabout 120.

The recurring units of formula I are derivatives of one or moreiodothyronine compounds selected from the group consisting of 3-T₁,3,3'-T₂, 3,5-T₂, rT₃, T₃ and T₄ as defined in Table I below.

                  TABLE I                                                         ______________________________________                                        3,3',5,5'-Tetraiodothyronine                                                                          T.sub.4                                               3,3',5-Triiodothyronine T.sub.3                                               3,3',5'-Triiodothyronine                                                                              rT.sub.3                                              3,5-Diiodothyronine     3,5-T.sub.2                                           3,3'-Diiodothyronine    3,3'-T.sub.2                                          3-Monoiodothyronine     3-T.sub.1                                             ______________________________________                                    

When the iodothyronine polymers of the present invention are used totreat thyroid hormone deficiencies, substantially all of the recurringunits of formula I are the physiologic L-stereroisomer. That is, atleast 90%, preferably 95%, and most preferably greater than 99% of therecurring units are the physiologic L-stereoisomer. In the iodothyroninepolymers used to treat thyroid hormone deficiencies, the recurring unitsof formula I are derivatives of the pharmacologically activeiodothyronine compounds identified in Table II.

                  TABLE II                                                        ______________________________________                                        3,3',5,5'-Tetraiodo-L-                                                                          Thyroxine    LT.sub.4                                       thyronine                                                                     3,3',5-Triiodo-L-thyronine                                                                      Liothyronine LT.sub.3                                       3,3',5'-Triiodo-L-thyronine                                                                     Reverse T.sub.3                                                                            rLT.sub.3                                      3,3'-Diiodo-L-thyronine                                                                         --           3,3'-LT.sub.2                                  ______________________________________                                    

In one embodiment of the invention the iodothyronine polymer is ahomopolymer as defined below in Table III.

                  TABLE III                                                       ______________________________________                                                   Substitution in Formula I                                          Abbreviation A     B           C   D                                          ______________________________________                                        poly-T.sub.4 I     I           I   I                                          poly-T.sub.3 I     I           I   H                                          poly-rT.sub.3                                                                              I     H           I   I                                          poly-3,5-T.sub.2                                                                           I     I           H   H                                          poly-3,3'-T.sub.2                                                                          I     H           I   H                                          poly-3-T.sub.1                                                                             I     H           H   H                                          ______________________________________                                    

In each such homopolymer, substantially all of the recurring units willbe those identified above. That is, at least 90%, preferably at least95%, and most preferably at least 99% of the recurring units of eachhomopolymer will contain the substituents identified in Table III. Theiodothyronine homopolymers in which substantially all of the recurringunits of formula I are L-stereoisomers and in which A, B, C and D areiodo, or in which A, B and C are iodo and D is H have utility in thetreatment of thyroid hormone deficiency. The preferred homopolymers foruse in therapy are poly-LT₄ and poly-LT₃.

The iodothyronine polymers of the present invention in whichsubstantially all of the recurring units of formula I areL-stereoisomers and A and C are iodo and B and D are independently H oriodo have utility in the treatment of thyroid hormone deficiencies inhuman and other mammals. LT₄ is the primary thyroid hormone in mammals,but LT₃ is also released by the thyroid gland and is also active as athyroid hormone. LT₄ and LT₃ are found in the blood in an approximate4:1 ratio. In one embodiment of the present invention, theiodo-thyronine polymer contains recurring units derived from both LT₄and LT₃ to form a copolymer of these units. Preferably, from about 70 toabout 90% of the recurring units are the LT₄ derivatives and about 10 toabout 30% of the recurring units are the LT₃ derivatives. Mostpreferably, the ratio is approximately 4:1 i.e. about 80% of therecurring units are LT₄ and approximately 20% of such units are LT₃.This copolymer is referred to herein as poly-LT₄ /LT₃.

It has been found that rLT₃ may also have a role in thyroid hormonefunction in humans and other mammals. A further aspect of the presentinvention provides an iodothyronine polymer in which a fraction of therecurring units are derived from rLT₃. In such an iodothyronine polymer,approximately 70-89% of the recurring units are derived from LT₄,approximately 10-29% of the recurring units are derived from LT₃, andthe remainder of the recurring units are derived from rLT₃. Mostpreferably, approximately 80% of such units are derived from LT₄,approximately 15% of such units are derived from LT₃, and approximately5% of such units are derived from rLT₃. This heteropolymer is referredto herein as poly-LT₄ /LT₃ /rLT₃.

A further aspect of the present invention provides iodothyroninepolymers which contain further recurring units of formula II ##STR3## inwhich R is a residue of any of the amino acids commonly found in nature.These amino acids are listed by Lehninger in Principles of Biochemistry(1982) published by Worth Publishers Inc of New York (see page 96) asalanine, arginine, asparagine, aspartic acid, cysteine, glutamine,glutamic acid, glycine, histidine, isoleucine, leucine, lysine,methionine, phenylalanine, proline, serine, threonine, tryptophan,tyrosine and valine. The properties of the iodothyronine polymers aremodified by copolymerization with these amino acids. For example, ifgreater aqueous solubility is desired, hydrophilic amino acids, likelysine, arginine, aspartic acid, glutamic acid, serine or threonine canbe copolymerized into the polypeptide chain. The amount of amino acidincorporated will be dependent upon the particular iodothyronine/aminoacid copolymer(s), and the properties desired. The recurring units offormula II may comprise up to 50%, preferably up to 66%, most preferablyup to 80% of the recurring units in the copolymers.

Iodothyronine polymers of the present invention in which substantiallyall of the recurring units of formula I are the L-stereoisomers and inwhich the recurring units are of formula I in which A and C are iodo andB and D are independently H or iodo have utility in the treatment ofthyroid hormone deficiencies. A further aspect of the present inventiontherefore provides a pharmaceutical composition suitable for treatingthyroid hormone deficiencies which comprises a pharmaceuticallyacceptable diluent or carrier and a pharmacologically active ingredientconsisting of a pharmaceutically effective amount of a substantiallypure synthetic iodothyronine polymer having a plurality of recurringunits, which may be the same or different, of the formula I in which Aand C are iodo and B and D are independently H or iodo, in which polymersubstantially all of the recurring units of formula I areL-stereoisomers. Preferably at least one of B or D is iodo. The averagenumber of the recurring units may vary from about 5 to about 400,preferably from about 10 to about 400, more preferably from about 20 toabout 200, or from about 30 to about 150 or from about 80 to about 120.The iodothyronine polymer in these pharmaceutical compositions may bepoly-LT₄, poly-LT₃, poly-LT₄ /LT₃, poly-LT₄ /LT₃ /rLT₃ or mixturesthereof. Particularly preferred compositions are those in which theiodothyronine polymer is poly-LT₄, poly-LT₃, a mixture of poly-LT₄ andpoly-LT₃ in which the ratio of poly-LT₄ to poly-LT₃ lies in the range7:3 to 9:1 preferably about 4:1 or a mixture of poly-LT₄ poly-LT₃ andpoly-rLT3 in which the ratio of poly-LT₄ to poly-LT₃ and poly-rLT₃ isapproximately 80:15:5.

In therapeutic use, the iodothyronine polymer is preferably administeredorally. Thus the therapeutic compositions of the present invention maytake the form of any of the known pharmaceutical compositions for oraladministration. Pharmaceutically acceptable carriers are well known inthe art of pharmacy. The compositions of the invention may contain0.1-90% by weight of iodothyronine polymer. The compositions of theinvention are generally prepared in unit dosage form.

Compositions for oral administration are the known pharmaceutical formsfor such administration, for example tablets, capsules, syrups andaqueous or oily suspensions. The diluent or carrier used in thepreparation of these compositions can be any of the materials known inthe pharmacists' art. Tablets may be prepared by mixing theiodothyronine polymer with an inert diluent such as calcium phosphate inthe presence of disintegrating agents, for example maize starch, andlubricating agents, for example magnesium stearate, and tableting themixture by known methods. The tablets may be formulated in a mannerknown to those skilled in the art so as to give a sustained release ofthe compounds of the present invention. Such tablets may, if desired, beprovided with enteric coatings by known methods, for example by the useof cellulose acetate phthalate. Similarly, capsules, for example hard orsoft gelatin capsules, containing the active compound with or withoutadded excipients, may be prepared by conventional means and, if desired,provided with enteric coatings in a known manner. The tablets andcapsules may conveniently each contain 12.5 to 500 microgrammes of theiodothyronine polymer. Other compositions for oral administrationinclude, for example, aqueous suspensions containing the iodothyroninepolymer in an aqueous medium in the presence of a non-toxic suspendingagent such as sodium carboxymethylcellulose, and oily suspensionscontaining a compound of the present invention in a suitable vegetableoil, for example arachis oil.

An alternative route of administration of the iodothyronine polymer isby means of an implant. In this case a pellet containing iodothyroninepolymers containing large numbers of recurring units is implanted underthe skin of the patient and pharmacologically active amounts of theiodothyronine polymer are then released over an extended period of time,suitably over several weeks or months.

In some formulations it may be beneficial to use the compounds of thepresent invention in the form of particles of very small size, forexample as obtained by fluid energy milling.

The pharmaceutical compositions containing a therapeutically effectiveamount of the iodothyronine polymers of the present invention in whichsubstantially all of the recurring units of formula I are theL-stereoisomers may be used to treat thyroid hormone deficiencies inwarm blooded animals including human beings. In such treatment theamount of the iodothyronine polymer administered per day is under thecontrol of the prescribing physician and will depend inter alia on theage of the patient and on the severity of the condition to be treatedbut will usually lie in the range 12.5 to 1000 micrograms per day,preferably 25 to 400 micro-grams per day, most preferably 50 to 300micrograms per day given in single or divided doses at one or more timesduring the day. In the case of iodothyronine polymers containingrecurring units of formula II, the amount of the polymer administeredmay be higher than quoted above but will be such as to give rise toequivalent amounts of the pharmacologically active iodothyroninemoieties.

A preferred method of synthesizing the iodothyronine polymers of thepresent invention comprises the polymerisation of one or moreN-carboxyanhydrides (NCA) of formula III ##STR4## in which A is iodo,and B, C, and D are H or iodo. Suitable N-carboxyanhyrides of formulaIII are identified in Table IV.

                  TABLE IV                                                        ______________________________________                                                   Substitution in Formula III                                        Abbreviation A     B           C   D                                          ______________________________________                                        T.sub.4 -NCA I     I           I   I                                          T.sub.3 -NCA I     I           I   H                                          rT.sub.3 -NCA                                                                              I     H           I   I                                          3,5-T.sub.2 -NCA                                                                           I     I           H   H                                          3,3'-T.sub.2 -NCA                                                                          I     H           I   H                                          3-T.sub.1 -NCA                                                                             I     H           H   H                                          ______________________________________                                    

When the desired iodothyronine polymer is one in which substantially allof the recurring units are in the same stereoisomeric form (preferablythe L-stereoisomeric form), the N-carboxyanhydride of formula III shouldbe substantially all in that same stereoisomeric form.

When the desired iodothyronine polymer is a homopolymer, oneN-carboxyanhydride of formula III is used. However, if the desirediodothyronine polymer is a copolymer or heteropolymer, then two or moreN-carboxyanhydrides of formula III are used in the same molarproportions as is desired in the iodothyronine polymer. For example,when the desired iodothyronine polymer is a copolymer of LT₄ and LT₃,the N-carboxy-anhydrides of LT₄ and of LT₃ are used in the molar ratiodesired in the iodothyronine copolymer and when the desirediodothyronine polymer is a heteropolymer of LT₄, LT₃ and rLT₃, theN-carboxyanhydrides of LT₄, LT₃ and rLT₃ are used in the molar ratiodesired in the final copolymer. When the iodothyronine polymer alsocontains one or more further recurring units of formula II, anN-carboxyanhydride of formula IV ##STR5## may be used in addition to theN-carboxyanhydride of formula III. The N-carboxyanhydrides of formulaIII and formula IV are used in the molar ratio desired in the finaliodothyronine polymer.

The polymerization preferably comprises reacting one or more compoundsof formula III in an anhydrous solvent, preferably at a concentration ofabout 5-40% and a temperature from about 0° C. to the boiling point ofthe solvent for sufficient time to complete the polymerisation. Thereaction is continued until polymerisation is complete as indicated, forexample, by product precipitation, cessation of CO₂ evolution, theattainment of maximum viscosity or the absence of the starting material,as indicated for example, by spectroscopic examination of the reactionmixture. Examples of suitable anhydrous solvents include ethers, such asdioxane or tetrahydrofuran, aromatic solvents, such as benzene,chlorobenzene, and toluene, and other solvents, such as dimethylformamide, ethyl acetate and dimethyl sulphoxide. A preferred solvent isdioxane or tetrahydrofuran.

Preferably, a base is used as an initiator in the above reaction. Aninorganic or organic base may be used, although an organic base ispreferred. Examples of suitable bases include organic amines such asn-butylamine, triethylamine, tributylamine, triamylamine,diisopropylethylamine or alkali metal alkoxides such as sodium methoxideor sodium ethoxide. The molar ratio of the N-carboxyanhydride derivativeof formula III to the initiator lies in the range 20 to 400 preferably30 to 150 more preferably 50 to 100. Most preferably, the base is sodiummethoxide.

The iodothyronine polymers of the present invention may be prepared bythe further iodination of iodothyronine polymers having recurring unitsof formula I in which A is iodo, B is H or iodo and C and D are H. Theseiodothyronine polymer starting materials are identified in Table III aspoly-3,5-T₂ and poly-3-T₁ respectively. If these polymers are subjectedto vigorous iodination conditions, for example by the use of excesspotassium triiodide or of iodine monochloride as the iodinating agent,iodothyronine polymers can be produced in which both C and D are iodo.Thus poly-3,5-LT₂ gives poly-LT₄ and poly-3-LT₁ , gives poly-rLT₃. Byusing less vigorous iodination conditions, for example potassiumtriiodide in diethylamine, it is possible to produce iodothyroninepolymer in which C is iodo and D is H. Thus poly-3,5-LT₂ would givepoly-LT₃ and poly-3-LT₁ would give poly-3,3'-LT₂. By choosing iodinationconditions in which iodination is incomplete, for example by restrictingthe amount of iodinating agent, it is possible to produce iodothyroninepolymers in which C is iodo and in which D is iodo in only some of therecurring units. For example, copolymers of LT₄ and LT₃ may be preparedby partial iodination of poly-3,5-LT₂.

The iodothyronine polymers of the present invention may also be preparedby the condensation of the amino acids from which the recurring units offormula I are derived in the presence of a dehydrating agent such asdicyclohexylcarbodiimide which is converted into dicyclohexylurea whenit removes the elements of water from two amino acid residues to form apeptide bond between them. Copolymers and hetero-polymers may beprepared by condensing mixtures of two or more amino acids.

Homogeneous polymerizations to form hetero-polymers result in a randomdistribution of each component in the polymer. However, whensequence-specific copolymer or heteropolymer combinations are desired, asolid phase synthesis of the Merrifield type is useful. The preferredmethod of synthesis is through the t-BOC or f-MOC intermediates of theiodothyronines and other amino acids if applicable. Synthesis proceedsas previously described in Groginski, Amer. Biotech. Lab.,May/June:38-51 (1986), incorporated herein by reference.

The N-carboxyanhydride of formula III may be prepared by reacting theappropriate iodothyronine with a carbonylating reagent to form theN-carboxyanhydride. More particularly, they are synthesized by reactinga compound represented by the formula V ##STR6## or a salt thereof witha carbonylating reagent and recovering the reaction product. Preferably,the reaction takes place in the presence of an anhydrous solvent, suchas tetrahydrofuran (THF), but other appropriate solvents known to thoseskilled in the art can be used. A preferred carbonylating reagent ishexachlorodimethylcarbonate, (CCl₃ O)₂ CO. This normally solid chemicalis commercially available from Aldrich Chemicals under the trade nameTriphosgene. Typically, the iodothyronine is suspended in the anhydroussolvent and the hexachlorodimethylcarbonate is added. An excess of thehexachlorodimethylcarbonate is used. Alternatively, phosgene gas may beused as the carbonylating agent.

After it has been prepared the iodothyronine polymer may be precipitatedand the resulting solid collected by filtration and may be furtherpurified, if necessary, by recrystallisation. The product isadvantageously dried by lyophilisation. In this process the precipitatediodothyronine polymer, if necessary following recrystallisation, isprefrozen or frozen in situ by evaporative cooling in vacuo withsufficient external heat provided to obtain a product with the desired,preferably less than 0.1%, moisture content.

The N-carboxyanhydrides of formula III obtained by the above synthesisare typically recrystallised to obtain intermediates of pharmaceuticalpurity. Since the prepared anhydrides are moisture sensitive, specialcare to ensure anhydrous conditions of the reaction, recovery andstorage of the N-carboxyanhydrides is important. This syntheticprocedure may also be used to prepare the N-carboxyanhydride derivativesof formula IV for copolymerization or heteropolymerisation with theN-carboxyanhydride derivatives of formula III to prepare iodothyroninepolymers having further recurring units of formula II.

Compounds of formula V are prepared by methods which are well known inthe art such as those described, for example, in U.S. Pat. Nos.2,579,668, 2,886,592, 2,889,363, 2,889,364, 3,477,954 and 3,577,535.

The iodothyronine polymers of the present invention provide a method ofdelivering thyroid hormones to a patient in need thereof. Because thethyroid hormones are released by digestive proteolysis of theiodothyronine polymers of this invention, it is expected that the use ofthe iodothyronine polymers would have a long physiologic effect becauseof the sustained release from the polymers of the monomeric thyroidhormones. The use of copolymers containing recurring units derived fromtwo or more thyroid hormones or mixtures of homopolymers of the thyroidhormones in the appropriate ratio provides a means whereby the naturallyoccurring ratio of thyroid hormones may be duplicated. Attempts havebeen made before to duplicate this naturally occurring ratio byadministering a mixture of LT₃ and LT₄ (see for example U.S. Pat. Nos.3,477,954 and 3,577,535). However, LT₃ has a short half life in theblood compared to the half life of LT₄ and so the desired ratio cannotbe maintained over a long period of time. The iodothyronine polymers ofthe present invention are solid materials which may be readily handledand formulated to give stable, consistent pharmaceutical compositionsfor the treatment of thyroid hormone deficiencies.

The invention will now be illustrated by the following Examples.

EXAMPLE 1

Hexachlorodimethylcarbonate (10 g) was added to a suspension of3,5-diodo-L-thyronine (26.3) in anhydrous tetrahydrofuran (125 ml) andthe mixture was heated to 67° C. for 15 minutes. Anhydroustetrahydrofuran (500 ml) and then anhydrous hexane (3000 ml) were addedand the mixture stored at 20° C. for three hours. 3,5-Diodo-L-thyronineN-carboxyanhydride (3,5-LT₂ -NCA) was collected by filtration. Yield 24g.

EXAMPLE 2

A solution of 3,5-diiodo-L-thyronine N-carboxy-anhydride (1 g) indioxane (10 ml) was stirred rapidly and a 1% solution of sodiummethoxide in methanol (0.05 ml) was added. The mixture was stirred forsix days at ambient temperature and then petroleum ether (20 ml) wasadded and the resulting slurry triturated with petroleum ether.Polymeric 3,5-diodo-L-thyronine (poly 3,5-LT₂) was collected byfiltration and dried in vacuo. Yield 0.96 g.

EXAMPLE 3

In a similar manner to that described in Example 1, 3,3',5-triiodo-L-thyronine N-carboxyanhydride (LT₃ -NCA) was prepared in 65%yield and polymerised to give polymeric 3,3 ', 5-triodo-L-thyronine(poly-LT₃) in 62% yield in a similar manner to that described in Example2.

EXAMPLE 4

In a similar manner to that described in Example 1,3,3',5,5'-tetraiodo-L-thyronine (LT₄ -NCA) was prepared in 22% yieldfrom 3,3', 5,5'-tetraiodo-L-thyronine which had been dried in vacuo at100° C. for 17 hours and then polymerised to give polymeric3,3',5,5'-tetraiodo-L-thyronine (poly-LT₄) in 82% yield in a similarmanner to that described in Example 2.

EXAMPLE 5

In a similar manner to that described in Example 1,3,5,5'-triiodo-L-thyronine N-carboxyanhydride (rLT₃ -NCA) was preparedin 51% yield and polymerised to give polymeric 3,5,5'-triodo-L-thyronine(poly-rLT₃) in 70% yield in a similar manner to that described inExample 2.

EXAMPLE 6

A mixture of 4 parts of 3,3', 5,5'-tetraiodo-L-thyronineN-carboxyanhydride (LT ₄ -NCA) prepared in a similar manner to thatdescribed in Example 1 and 1 part of 3,3', 5-triiodo-L-thyronineN-carboxyanhydride (LT₃ -NCA) prepared in a similar manner to thatdescribed in Example 3 was polymerised in a similar manner to thatdescribed in Example 2 to give a polymer containing recurring unitsderived from both LT₃ and LT₄ (poly LT₄ /LT₃) in 62% yield.

EXAMPLE 7

A mixture of 80 parts 3,3', 5,5'-tetraiodo-L-thyronineN-carboxyanhydride (LT₄ -NCA) prepared in a similar manner to thatdescribed in Example 4, 15 parts of 3,3', 5-triiodo-L-thyronineN-carboxyanhydride (LT₃ -NCA) prepared in a similar manner to thatdescribed in Example 3 and 5 parts of 3,5,5'-triiodo-L-thyronineN-carboxyanhydride (rLT₃ -NCA) prepared in a similar manner to thatdescribed in Example 5 was polymerised in a similar manner to thatdescribed in Example 2 to give a heteropolymer containing recurringunits derived from LT₄, LT₃ and rLT₃ (poly LT₄ /LT₃ /rLT₃). The productwas precipitated from the reaction mixture by addition of petroleumether (2 volumes) and the precipitate dried in vacuo. Yield 55%.

EXAMPLE 8

Polymeric 3,5-diiodo-L-thyronine (poly-3,5-LT₂ -22 g prepared in asimilar manner to that described in Example 2) was dissolved in a 33%aqueous solution of diethylamine at 16° to 22° C. A 1.9N iodine solutionin concentrated aqueous potassium iodide solution (88 ml) was added withstirring. The mixture was stirred at 4° to 10° C. for 2 hours. Aprecipitate formed which was collected by filtration and washed withwater. The filter cake was dissolved in a mixture of ethanol (25 ml) and2N aqueous sodium hydroxide solution (100 ml). 2N Hydrochloric acid wasadded to neutralise the solution and a precipitate formed which wascollected by filtration and washed with water. The wet filter cake wasplaced in a freeze drying chamber in vacuo (less than 0.3 mm Hg) tofreeze the cake via evaporative cooling. Sufficient heat was provided(shelf temperature 40° C.) to reduce the moisture content to less than0.1% in 24 hours. The product was polymeric 3,3',5,5'-tetraiodo-L-thyronine. Yield 27 g.

EXAMPLE 9

Polymeric 3,5-diiodo-L-thyronine (poly-3,5-LT₂ -18.4 g prepared in asimilar manner to that described in Example 2) was dissolved in 33%aqueous diethylamine (185 ml). A solution of potassium triiodide 82 mlof a solution prepared from iodine (26.2 g), potassium iodide (67.8 g)and water (90 ml)! was added with stirring over 30 minutes. Stirring wascontinued for 15 minutes and water (111 ml) and then 2N hydrochloricacid were added to cause precipitation. The brown precipitate wascollected by filtration and the filter cake dissolved in a mixture ofethanol (1332 ml) and 1N aqueous sodium hydroxide solutions (111 ml).The solution was filtered, heated to boiling and treated with 30%aqueous acetic acid until precipitation commenced. The mixture wascooled in ice and the precipitate collected by filtration and washedwith water. The wet filter cake was placed in a freeze drying chamber invacuo (less than 0.3 mm Hg) to freeze the cake via evaporative cooling.Sufficient heat was provided (shelf temperature 40° C.) to reduce themoisture content to less than 0.1% in 24 hours. (Yield 24.6 g).

The product was hydrolysed with acid and high performance liquidchromatography (HPLC) of the hydrolysed product showed the presence of83.3% LT₄, 16.4% LT₃ and less than 0.1% of 3,5-LT₂ indicating that theproduct was a polymer containing recurring units derived from LT₄ andLT₃ (poly LT₄ /LT₃).

EXAMPLE 10

In a similar manner to that described in Example 8, polymeric3-iodo-L-thyronine (poly-3LT₁) was diiodinated to give polymeric3,5,5'-triiodo-L-thyro-nine (poly-rLT₃) in 96% yield. Polymeric3-iodo-L-thyronine was prepared in a similar manner to that described inExample 2 by polymerisation of 3-iodo-L-thyronine N-carboxyanhydride(3-LT₁ -NCA) which was prepared in 93% yield in a similar manner to thatdescribed in Example 1.

EXAMPLE 11

Direct co-polymerization of LT₄ and glycine was effected by suspending3,3', 5,5'-tetraiodo-L-thryonine (3.88 g) and glycine (Zwitterionicforms) (0.37 g) in anhydrous dioxane (50 ml). Dicyclohexylcarbodiimide(2.47 g) was added with stirring and the reaction was stirred for 4 daysat 17° -22° C. Acetic acid (0.2 ml) was added to decompose excessdicyclohexylcarbodiimide and petroleum ether (50 ml) was added toprecipitate the polymeric product. The product was collected byfiltration and the filter cake triturated with ethanol. The polymericproduct was dried in vacuo. Yield 5.22 g. HPLC analysis of the acidhydrolysis of the product showed a 50/50 mixture of LT₄ and glycine.

EXAMPLE 12

Boc-protected LT₄ and glycine are prepared as described in Tam et al.,Int. J. Peptide Protein Res., 21:57 (1983), and polymerized by standardsequential additions on polystyrene beads as an immobilized support. Thefollowing coupling sequence is used as described in Spatola, Amer.Biotech Lab., Dec. 14-22 (1984).

    ______________________________________                                        Stage    Reagent         Repeat  Time                                         ______________________________________                                        1        Methylene chloride                                                                            5       1                                            2        TFA             1       5                                            3        TFA             1       25                                           4        Methylene chloride                                                                            4       1                                            5        Diisopropylethylamine                                                                         2       2                                            6        Methylene chloride                                                                            3       1                                            7        DMF             3       1                                            8        Boc-glycine     --      1                                            9        DCC             --      --                                           10       DMF             1       1                                            11       Methylene chloride                                                                            3       1                                            12       Ethanol         3       1                                            13       DMF             3       1                                            14       Boc--LT.sub.4   --      1                                            15       DCC             --      --                                           16       DMF             3       1                                            17       Methylene chloride                                                                            3       1                                            18       Ethanol         3       1                                            ______________________________________                                    

Steps 7 through 18 are repeated 25 or more times to obtain a polymer of50 or more residues in length. Finally, the copolymer is isolated bycleavage from the resin using HF. The copolymer formed by this reactionhas alternating recurring units derived from LT₄ and glycine.

EXAMPLE 13

Hexachlorodimethylcarbonate (20 g) was added to a suspension of thesodium salt of 3,5-diodo-L-thyronine (52.6 g) which had been dried at100° C. in vacuo for 24 hours in anhydrous tetrahydrofuran (250 ml) andthe mixture was heated to 65° C. The reaction mixture was allowed toreact for five minutes and the solvent was then removed by evaporation.Anhydrous ethyl acetate (50 ml) and then anhydrous dichloromethane (140ml) were added and the mixture cooled at 4° C. for one hour.3,5-Diodo-L-thyronine N-carboxyanhydride (3,5-LT₂ -NCA) was collected byfiltration, washed with anhydrous hexane and dried in vacuo withoutheating. Yield 37.6 g.

EXAMPLE 14

A solution of 3,5-diiodo-L-thyronine N-carboxy-anhydride (37.2 g) inethyl acetate (372 ml which had been dried over potassium carbonate) wasstirred rapidly and a 1% solution of sodium methoxide in methanol (1.86ml) was added. The mixture was stirred for four days at ambienttemperature temperature and then polymeric 3,5-diodo-L-thyronine (poly3,5-LT₂) was collected by filtration, washed with ethyl acetate and thenhexane and dried in vacuo. Yield 24.9 g.

EXAMPLE 15

Polymeric 3,5-diodo-L-thyronine (0.715 g) was ground to a fine powderand dissolved with gentle warming in a mixture of dimethylformamide (8.6ml), water (5.7 ml) and diethylamine (4.3 ml) and the solution wascooled to 5°-10° C. A solution of potassium triodide was prepared fromiodine (31.5 g) and a 40% solution of potassium iodide in water (100 mlof solution). Four portions of the resulting solution (0.8 ml each) wereadded over 30 minutes. The reaction mixture was stirred overnight as thetemperature rose to ambient and then poured into acetone (200 ml). Asolid was collected by filtration and washed with degassed water. Thewashed solid was frozen on dry ice and lyophilised under vacuum (lessthan 0.3 mm Hg) using a shelf temperature of 35° C. to give polymeric3,3',5-triodo-L-thyronine (poly-LT₃). Yield 0.9 g.

EXAMPLE 16

Polymeric 3,5-diido-L-thyronine (1 g) was ground to a fine powder anddissolved with gentle warming in dimethylformamide (5 ml). A mixture ofglacial acetic acid (2 ml) and iodine monochloride (0.8 g) was addedover twenty minutes with rapid mixing and the resulting mixture heatedto 60° C. Glacial acetic acid (5 ml) and then water (12 ml) were addeddropwise and the mixture was reheated to 60° C. Potassium bisulphite(0.3 g) was added and the mixture cooled in ice. The resultingprecipitate was collected by filtration and washed with water. Thewashed solid was frozen on dry ice and lyophilised under vacuum (lessthan 0.3 mm Hg) using a shelf temperature of 35° C. to give polymeric3,3', 5,5'-tetraiodo-L-thyronine (poly-LT₄). Yield 1.56 g.

EXAMPLE 17

Hexachlorodimethylcarbonate (2 g) was added to a suspension of thesodium salt of 3,3', 5-triiodo-L-thyronine (6.73 g) which had been driedat 100° C. in vacuo for 24 hours in anhydrous tetrahydrofuran (25 ml)and the mixture was heated to 65° C. The reaction mixture was allowed toreact for ten minutes and the solvent was then removed by evaporation.Anhydrous ethyl acetate (7 ml) was added to dissolve the residue andthen anhydrous dichloromethane (20 ml) was added and the mixture cooledat 4° C. for one hour. 3,3', 5-Triiodo-L-thyronine N-carboxyanhydride(LT₃ -NCA) was collected by filtration, washed with anhydrous hexane anddried in vacuo without heating. Yield 2.8 g.

EXAMPLE 18

A solution of 3,3', 5-triiodo-L-thyronine N-carboxyanhydride (1.0 g) inanhydrous dioxane (10 ml) was stirred rapidly and a 1% solution ofsodium methoxide in methanol (0.05 ml) was added. The mixture wasstirred for four days at ambient temperature and then water (10 ml) wasadded with vigorous stirring. Polymeric 3,3', 5-triiodo-L- thyronine(poly-LT₃) was collected by filtration and washed with water. The washedsolid was frozen on dry ice and lyophilised under vacuum (less than 0.3mm Hg) using a shelf temperature of 35° C. Yield 0.68 g.

EXAMPLE 19

A suspension of the sodium salt of 3,3', 5,5'-tetraiodo-L-thyronine(1.55 g) which had been dried at 100° C. in vacuo for 24 hours inanhydrous tetra-hydrofuran was cooled and hexachlorodimethylcarbonate(0.4 g) was added. The mixture was heated to 50° C. for five minutes andthe solvent removed by evaporation. The residue was treated withanhydrous ethyl acetate (10 ml) and then with anhydrous dichloromethaneand was then cooled in ice. 3,3', 5,5'-Tetra-iodo-L-thyronineN-carboxyanhydride (LT₄ -NCA) was collected by filtration, washed withanhydrous hexane and dried in vacuo without heating. Yield 0.7 g.

EXAMPLE 20

A solution of 3,3', 5,5'-tetraiodo-L-thyronine N-carboxvanhydride (1.0g) in anhydrous dioxane (10 ml) was stirred rapidly and a 1% solution ofsodium methoxide in methanol (0.05 ml) was added. The mixture wasstirred for four days at ambient temperature and then water (10 ml) wasadded with vigorous stirring. Polymeric 3,3', 5,5'-tetraiodo-L-thyronine (poly-LT₄) was collected by filtration and washed with water.The washed solid was frozen on dry ice and lyophilised under vacuum(less than 0.3 mm Hg) using a shelf temperature of 35° C. Yield 0.21 g.

EXAMPLE 21

The following preparation is suitable for oral administration for thetreatment of thyroid hormone deficiency:

    ______________________________________                                        Component             Amount                                                  ______________________________________                                        1       Iodothyronine polymer                                                                           10 to 300 μg                                                               (dose dependent)                                    2       Corn Starch       30 mg                                               3       Lactose           61 mg                                               4       Polyvinylpyrrolidone (PVP)                                                                       4 mg                                               5       Talcum             5 mg                                               6       Sodium ascorbate   5 mg (antioxidant)                                 ______________________________________                                    

The finely powdered iodothyronine polymer is blended to uniformity withcorn starch, lactose, PVP and ascorbate, mixed into an aqueous pastewith 1.0 ml H₂ O and freeze dried (30° shelf temperature, 0.03 mm Hg).The resulting powder is mixed uniformly with talcum and pressed intotablets.

EXAMPLE 22

Hypothyroid male rats which were 2 months old and had an average weightof 95 g were prepared by surgical removal of the thyroid gland. Six toeight weeks were allowed for clearance of endogenous thyroid hormonesand rats were bled from the tail vein and serum levels of LT₃ and LT₄were measured by radioimmunoassay (RIA). Rats having high levels of LT₄due to inadequate thyroidectomy were removed from the study. A control,untreated group of four thyroidectomized rats was used to test forthyroid remnant regeneration during the course of the experiment. Thetreatment group of six rats received 10 μg/day of the iodothyroninepolymer (poly-T₄ /T₃) prepared in Example 9 slurried in corn syruporally by gavage. After 8 days of treatment, serum levels of LT₃ and LT₄were again measured by RIA. The results obtained are shown below inwhich the amounts of LT₄ and LT₃ are shown in nanograms per deciliter ofblood and the values quoted are the mean values for the groups ofanimals.

    ______________________________________                                                Before Treatment  After Treatment                                             LT.sub.3                                                                            LT.sub.4    LT.sub.3                                                                              LT.sub.4                                            (ng/dl)                                                                             (μg/dl)  (ng/dl) (μg/dl)                                  ______________________________________                                        Control   22      0.80        34    0.88                                      Treatment 26      <0.28       284   16.7                                      ______________________________________                                    

Since the establishment of adequate blood levels of thyroid hormones isa necessary and sufficient prerequisite for the euthyroid condition, weconcluded that these data demonstrate that the oral administration ofthe copolymer of LT₄ and LT₃ can treat thyroid hormone deficienciesresulting from insufficient thyroidal release of thyroid hormones.

EXAMPLE 23

The sodium salt of 3,3', 5,5'-tetraiodo-L-thyronine was suspended inwater and dilute (1N) hydrochloric acid was added to give a pH ofbetween 4 and 5. The mixture was shaken for 5 minutes and the solidformed was collected by filtration, washed with water and dried undervacuo at a temperature in the range 30°-50° C. The solid was 3,3',5,5'-tetraiodo-L-thyronine.

3,3', 5,5'-Tetraiodo-L-thyronine (46.1 g) was suspended intetrahydrofuran (400 ml) in a metal foil-wrapped vessel. The mixture washeated at 50°-55° C. under slightly reduced pressure and solvent (100ml) was removed by distilltion. A further portion of tetrahydrofuran(100 ml) was added and the distillation repeated to collect a total of200 ml of solvent. A solution of hexachlorodimethylcarbonate (12 g) intetrahydrofuran (35 ml) was added at 55° C. over a period of twentyminutes and the mixture heated at 55° C. for 2 hours. A further portionof hexachlorodimethylcarbonate (6 g) in tetrahydrofuran (15 ml) wasadded over ten minutes and the mixture heated at 55° C. for 1.5 hours.The mixture was added to dry hexane (3.8l) at ambient temperature over20 minutes. A yellow solid was collected by filtration, washed withhexane and dried in vacuo at 42° C. Yield 42.7 g.

A sample (35 g) of the dried product was dissolved in a mixture of ethylacetate (240 ml) and tetrahydrofuran (90 ml) with warming. The mixturewas filtered through charcoal and the tetrahydrofuran removed bydistillation under reduced pressure. Additional ethyl acetate (100 ml)was added and 100 ml of solvent was removed by distillation underreduced pressure. This addition/distillation cycle was repeated twice.The volume was then reduced to 50 ml by evaporation and the solutionstored at 2° C. for two hours. The resulting solid was collected byfiltration, washed with ethyl acetate and dried in vacuo at 40° C. Thedried solid was dissolved in a mixture of ethyl acetate (170 ml) andtetrahydrofuran (90 ml). The solvent was removed by evaporation. Theresidue was dissolved in ethyl acetate (100 ml) and the solvent removedby evaporation. This dissolution/evaporation cycle was repeated and theresidue dissolved in ethyl acetate (100 ml). The volume was reduced to50 ml by evaporation and the solution stored at 2° C. for two hours. Theresulting solid was collected by filtration, washed with ethyl acetateand dried in vacuo at 40° C. to give 3,3', 5,5'-tetraiodo-L-thyronineN-carboxyanhydride. Yield 21.2 g.

A solution of 3,3', 5,5'-tetraiodo-L-thyronine N-carboxyanhydride (1 g)in dioxane (8 ml) was stirred at 50° C. in a metal-foil wrapped vessel.A portion (50 microliters) of a solution of sodium methoxide (67.2 mg)in methanol (10 ml) was added and the mixture stirred at 50° C. for 3.5hours and then a further portion (50 microliters) of the above sodiummethoxide solution was added and the mixture stirred at 50° C. for atotal of 23 hours. A solid was collected by filtration, washed withdioxane and dried in vacuo at 50° C. to give a dioxane-insolublefraction of polymeric 3,3', 5,5'-tetraiodo-L-thyronine. Yield 0.317 g.The filtrate was slowly added to hexane (25 ml) and the resulting solidcollected by filtration, washed with hexane and dried in vacuo at 50° C.to give a dioxane-soluble fraction of polymeric 3,3',5,5'-tetraiodo-L-thyronine. Yield 0.403 g.

EXAMPLES 24 to 27

Four solutions of 3,3', 5,5'-tetraiodo-L-thyronine N-carboxyanhydride (1g prepared in Example 23) in dioxane (10 ml) were prepared with warming.Four solutions of sodium methoxide in methanol were made up as follows:

    ______________________________________                                                   Wt of NaOMe                                                                              Volume of methanol                                      Ex         (mg)       (ml)                                                    ______________________________________                                        24         67.2       10                                                      25         134        10                                                      26         335        10                                                      27         670        10                                                      ______________________________________                                    

A sample (50 microliters) of one of these sodium methoxide solutions wasadded to each of the solutions of 3,3', 5,5'-tetraiodo-L-thyronineN-carboxyanhydride and the resulting mixtures were stored at 48°-50° C.for 23 hours. In Example 24 a further portion (50 microliters) of thesodium methoxide solution was added after 1 hour. The mixtures were thenstored at ambient temperature for 48 hours and the solid which had beenformed was collected by filtration and dried at 40° C. in vacuo to givedioxane-insoluble fractions of polymeric 3,3',5,5'-tetraiodo-L-thyronine. The yields were Ex 24 0.014 g, Ex 25 0.220g, Ex 26 0.260 g and Ex 27 0.290 g. The filtrates were added dropwise tohexane (15 ml) over 5 minutes. A precipitate formed which was allowed tosettle. The supernatant was removed by decantation and the residue driedin vacuo at 40° C. to give dioxane-soluble fractions of polymeric 3,3',5,5'-tetraiodo-L-thyronine as a yellow solid. Yield Ex 24 0.705 g, Ex 250.700 g, Ex 26 0.500 g and Ex 27 0.580 g.

EXAMPLE 28

A portion (10 microliters) of a solution of sodium methoxide (134 mg) inmethanol (2 ml) was added to a solution of 3,3',5,5'-tetraiodo-L-thyronine N-carboxy-anhydride (1 g prepared in Example23) in dioxane (10 ml) and the mixture heated at 50° C. for 24 hours.The reaction mixture was centrifuged (3000 rpm for 5 minutes) and thesupernatant removed by decantation. The residue was treated with dioxane(8 ml) and the resulting mixture centrifuged (3000 rpm for 5 minutes),and the residue was dried in vacuo at 38° C. to give polymeric 3,3',5,5'-tetraiodo-L-thyronine. Yield 0.485 g.

EXAMPLE 29

A portion (10 microliters) of a 16% solution ofN,N-diisopropylethylamine in dioxane was added to a solution of 3,3',5,5'-tetraiodo-L-thyronine N-carboxy-anhydride (1 g prepared in Example23) in dioxane (10 ml) and the mixture heated at 50° C. for 96 hours andthen centrifuged (3000 rpm for 5 minutes). The supernatant was removedby decantation and the residue washed with dioxane (4 ml) and dried invacuo at ambient temperature to give polymeric 3,3',5,5'-tetra-iodo-L-thyronine. Yield 0.56 g.

EXAMPLE 30

A portion (5 microliters) of a 17.2% w/v solution of sodium methoxide inmethanol was added to a solution of 3,3', 5,5'-tetraiodo-L-thyronineN-carboxy-anhydride (1 g prepared in Example 23) in dioxane (10 ml) andthe mixture heated at 50° C. for 20 hours. The volume of the reactionmixture was reduced to 3 to 4 ml and then the mixture was centrifuged(3000 rpm for 5 minutes) and the supernatant removed by decantation. Theresidue was washed with dioxane (1 ml) and water (2×2 ml) and thenslurried with water (10 ml) and then cooled to -78° C. and dried invacuo (0.1 mm Hg) to give polymeric 3,3', 5,5'-tetraiodo-L-thyronine.Yield 0.550 g.

EXAMPLE 31

A portion (5 microliters) of a 17/2% w/v solution of sodium methoxide inmethanol was added to a solution of 3,3', 5,5'-tetraiodo-L-thyronineN-carboxyanhydride (1 g prepared in Example 23) in tetrahydrofuran (10ml) and the mixture heated at 48° C. for 15 hours. Water was added toprecipitate a solid which was separated by decantation. A portion of thewet solid (XX g) was cooled to -78° C. and dried in vacuo (0.1 mm Hg) togive polymeric 3,3',5,5'-tetra-iodo-L-thyronine. Yield 0.300 g.

We claim:
 1. A substantially pure synthetic iodothyronine polymer having5 to 400 recurring units, which may be the same or different, of theformula I ##STR7## in which A is iodo and B, C and D are independently Hor iodo with a hydrogen atom at the N-terminus and a hydroxy group atthe C-terminus and N=5-400.
 2. An iodothyronine polymer as claimed inclaim 1 in which substantially all of the recurring units of formula Iare L-stereoisomers.
 3. An iodothyronine polymer as claimed in claim 1in which A and C are iodo and B and D are independently H or iodo.
 4. Aniodothyronine polymer as claimed in claim 3 in which at least one of Band D is iodo.
 5. An iodothyronine polymer as claimed in claim 1 inwhich the number of recurring units in the polymer is in the range 10 to400.
 6. The iodothyronine polymer of claim 1 in which A and C are bothiodo and in which B and D are both iodo in 70 to 90% of the monomers andonly one of B and D is iodo in the remaining 10 to 30% of the monomers.7. An iodothyronine polymer as claimed in claim 6 in which R is the sidechain from one or more amino acids selected from the group consisting oflysine, arginine, aspartic acid, glutamic acid, serine or threonine. 8.A pharmaceutical composition suitable for treating thyroid hormonedeficiencies comprising a pharmaceutically acceptable diluent or carrierand a pharmaceutically effective amount sufficient to raise blood levelsof thyroid hormones the polymer of claim 1, in which polymersubstantially all of the recurring units of formula I areL-stereoisomers with a hydrogen atom at the N-terminus and hydroxy groupat the C-terminus.
 9. The pharmaceutical composition of claim 8 in inwhich A and C are both iodo and in which B and D are both iodo in 70 to90% of the monomers and only one of B and D is iodo in the remaining 10to 30% of the monomers.
 10. A pharmaceutical composition as claimed inclaim 8, in which at least one of B or D is iodo.
 11. A pharmaceuticalcomposition as claimed in claim 8, in which the pharmacologically activeingredient comprises a mixture of pharmaceutically effective amounts ofa first iodothyronine polymer in which B, C and D are iodo and a secondiodothyronine polymer in which B and C are iodo and D is H.
 12. Apharmaceutical composition as claimed in claim 11, in which the molarratio of the amount of the first iodothyronine polymer to the amount ofthe second iodothyronine polymer lies in the range 7:3 to 9:1.
 13. Apharmaceutical composition as claimed in claim 11, which also comprisesa pharmaceutically effective amount sufficient to raise blood levels ofthyroid hormones, of a further iodothyronine polymer in which B is H andC and D are iodo.
 14. A pharmaceutical composition as claimed in claim13, in which the ratio of the amount of the first iodothyronine polymerto the amount of the second iodothyronine polymer to the amount of thefurther iodothyronine polymer is apporoximately 80:15:5.
 15. A method oftreating thyroid hormone deficiencies comprising administering to apatient a therapeutically effective amount of the syntheticiodothyronine polymer of claim 8 sufficient to raise levels of thyroidhormones.
 16. The method of claim 15 in which A and C are both iodo andin which B and D are both iodo in 70 to 90% of the monomers and only oneof B and D is iodo in the remaining 10 to 30% of the monomers.
 17. Amethod of treating thyroid hormone deficiencies as claimed in claim 15in which at least one of B or D is iodo.
 18. An N-carboxyanhydridecompound of formula III ##STR8## in which A is iodo and B, C and D areindependently H or iodo provided that at least one of B, C or D is H.19. The N-carboxyanhydride compound of claim 18 in which saidN-carboxyanhydride is an L-stereoisomer and in which A and C are iodoand at least one of B and D is iodo.
 20. An N-carboxyanhydride compoundas claimed in claim 19, in which A and C are iodo and at least one of Band D is iodo.